1. Field of the Invention
This invention relates to a small-sized printer suited for use in a desk-top electronic calculator or similar apparatus, and more particularly to an extremely useful small-size printer which is constructed so as to realize a sizable reduction of the number of parts. Low price, easy assembly, minimization of failure rate and repeated stable operations, and no adjustments in the manufacturing process nor any fine adjustments in use are realized.
More specifically, this invention relates to a small-sized printer in which electromagnet means is mounted to each printing hammer. The electromagnet means is composed of a pair of elastic members designed to pass electric current and arranged parallel to the axis of the type wheel, and is so constructed that when no printing occurs the paramagnetic material in said electromagnet means is attracted by a permanent magnet to bend the elastic members so as to store mechanical energy. When printing occurs an electric current sufficient to at least counteract the magnetic field of the permanent magnet is supplied to the electromagnet means to permit a particular hammer or hammers to hit the type wheel. In order to let the hammer return automatically and quickly to its original position without requiring any specific return mechanism, the magnetic field distribution of the permanent magnet is expanded to cover the entire scope of movement of the paramagnetic material in the hammer, or the paramagnetic material itself is moved within the span of the magnetic field.
2. Description of the Prior Art
Many of the heretofore known types of printers are designed for use in high-speed output machines such as large-sized computers, so that such printers are complicated in mechanism and large in size. There is, for example known a printer of the type in which each hammer operating shank is supported by a pair of leaf springs transversely disposed to the axis of the type wheel so that it is normally attracted by first electromagnet means, and in operation, the shank is released by the action of a second electromagnet means within the first electromagnet means to thereby allow printing. This type of printer, however, requires a specific cam mechanism for returning the shank to the home position, resulting in a complicated printer mechanism and high manufacturing cost. The present invention makes unnecessary such specific return mechanism. According to the present invention, in order to allow automatic return of each shank, the second electromagnet means is provided on each printing hammer and also the first magnet means is so arranged that its magnetic field will cover the entire scope of movement of the hammer.
There is also known a printer utilizing the principle of Fleming's left-hand rule by providing a second magnetic field generating means in the hammer assembly. This type of printer however involves fairly high voltage and current demands as it utilizes the interactions of magnetic fields opposed to the force of the return spring, and also the second magnetic field generating means is necessarily enlarged in size. Further, since the printing operation is based on horizontal movement of the shank supported by a pair of leaf springs planted vertical to the axis of the type wheel, a considerable space is required for the hammer assembly and hence size reduction of this type of printer can hardly be achieved by any significant degree. Moreover, the return stroke of the shank builds up a large volume of energy as the restorative force of the pair of leaf springs is added to the repulsive force of the shank, so that a specific buffer mechanism and stopper means are required. Also involved is the problem of difficult assembly as adjustment of the stroke length is indispensable.